This invention relates generally to drilling hammers, and in particular to downhole hammers for use in horizontal directional drilling operations.
During horizontal directional drilling operations hard soil or rock may impede the progress of borehole formation. Percussive tools driven by hammer assemblies are sometimes used to fracture such subterranean formations. However, there remains a need for improvement.
The present invention comprises a percussive tool for use with a dual-member drill string. The dual-member drill string comprises an outer member and an inner member. The inner member is rotatable independently of the outer member. The percussive tool comprises a housing connectable with the drill string and a drive member rotatably supported within the housing. The drive member is connectable with the inner member of the drill string. A hammer assembly is supported by the housing and operable in response to rotation of the drive member.
The present invention further comprises a percussive tool for use in a borehole. The tool comprises a housing and a drive member rotatably supported within the housing. A hammer assembly is supported by the housing. The hammer assembly comprises a hydraulic pump assembly and a hammer unit. The pump assembly operates in response to rotation of the drive member and is adapted to power operation of the hammer unit.
Still further, the present invention comprises a horizontal directional drilling machine. The horizontal directional drilling machine comprises a rotary drive system and a drill string. The drill string has a first end and a second end. The first end of the drill string is operatively connected to the rotary drive system. The drill string comprises a dual-member drill string having an outer member and an inner member. The inner member is independently rotatable of the outer member. A percussive tool comprising a hammer assembly is operatively connected to the second end of the drill string so that rotation of the inner member will drive operation of the tool.
Finally, the present invention includes a method of underground horizontal directional drilling. The method using a horizontal directional drilling machine. The horizontal directional drilling machine includes a rotary drive system and a dual-member drill string. The dual-member drill string has a first end and a second end. The rotary drive system is attached to the first end of the drill string. The drill string comprises an outer member and an inner member. The inner member is rotatable independently of the outer member. The machine further comprises a percussive tool. The percussive tool is attached to the second end of the drill string. A bit is supported on the percussive tool. The percussive tool comprises a hammer assembly for driving the bit. The method comprises operating the hammer assembly by rotating the inner members.